This invention relates to cable-making apparatus, and more specifically to apparatus for assemblying a cable by laying outer strands around an axial core while imparting reversing or pre-twist thereto. Still more specifically, the invention is directed to some improvements in such cable-making apparatus which are intended to afford smooth transmission of pre-twists through the lengths of the outer strands and the core from respective pay-out means to a laying die.
Cables are in use which have an axial core of a multiplicity of layed wires and an outer layer comprising a plurality of strands each composed also of a number of wires. In conventional apparatus for the manufacture of such cables, the above cable components are fed from respective pay-out reels or drums to a laying die while being pre-twisted. On emerging from the die, the laid assembly of the outer strands around the core is taken up around a take-up reel or drum.
A problem in this known type of cable-making apparatus is that the pre-twists imparted to the individual cable components are not smoothly transmitted therethrough from the respective pay-out reels to the laying die. The pre-twists tend to accumulate at those portions of the cable components laying immediately next to the pay-out reels, until the resulting kinks are swept forwardly. Cables produced in this manner lack uniformity in pitch and diameter along their length.
For guiding the outer strands from their pay-out reels to the laying die, for example, the prior art apparatus employs large-diameter pulleys in engagement with respective strands. These pulleys are serious impediments to the transmission of the pre-twists through the outer strands. Rollers disposed along the path of the core from its pay-out reel to the laying die in the prior art apparatus are also unsatisfactory for assuring smooth transmission of the pre-twist through the core.
Japanese Patent Publication No. 36052/1974 discloses the use of concave rollers for guiding each strand or the assembled cable around a circuitous path while inducing the same to rotate about its own axis. These concave guide rollers, however, are intended for use in cable-making machines of the "caged" or revolving frame type to which the noted Japanese patent is directed, with the rollers mounted in a revolving frame. Such concave rollers have proved quite unsatisfactory when employed for guiding each outer strand along a stationary, curved path in cable-makig apparatus of the type to which the instant invention is directed.
When incorporated in cable-making apparatus of the revolving frame type, the concave rollers are admittedly capable of effectively guiding a strand or a cable while inducing its rotation about its axis, thanks to a centrifugal effect exerted thereon. When employed for guiding a pre-twisted strand along a stationary, curved path, however, the concave rollers do not permit smooth transmission of the pre-twist through the strand. This is primarily because the angle between the axis of each concave roller and its circumference increases too rapidly from the midpoint toward the outer ends thereof.
Another problem in the prior art is that such guide rollers are made of metal such as steel with or without chromium plating. Such metal-made guide rollers do not offer sufficient frictional resistance to the strand travelling thereover for efficient transmission of the pre-twist therethrough.